Ignition inhibiting gas water heater

ABSTRACT

A gas water heater including a water container adapted to be heated by a gas burner; and an enclosure surrounding the burner, the enclosure having at least one entryway adapted to allow air and fumes to enter the enclosure without igniting flammable gases or vapors outside of the enclosure.

FIELD OF INVENTION

[0001] The present invention relates to arrangements to make gas firedwater heaters safer for use.

BACKGROUND OF INVENTION

[0002] The most commonly used gas-fired water heater is the storagetype, generally comprising an assembly of a water tank, a main gasburner to provide heat to the tank, a standing pilot burner to initiatethe main burner on demand, an air inlet adjacent the burner near thebase of the jacket, an exhaust flue and a jacket to cover thesecomponents. Another type of gas-fired water heater is the instantaneoustype which has a water flow path through a heat exchanger heated, again,by a main burner initiated from a pilot burner flame. For convenience,the following description is in terms of storage type water heaters butthe present invention is not limited to this type. Thus, reference to“water container,” “water containment and flow means,” “means forstoring or containing water” and similar such terms includes watertanks, reservoirs, bladders, bags and the like in gas-fired waterheaters of the storage type and water flow paths such as pipes, tubes,conduits, heat exchangers and the like in gas-fired water heaters of theinstantaneous type.

[0003] A particular difficulty with many locations for water heaters isthat they are also used for storage of other equipment such as lawnmowers, trimmers, snow blowers and the like. It is a common procedurefor such machinery to be refueled in such locations.

[0004] There have been a number of reported instances of spilledgasoline and associated fumes being accidently ignited. There are manyavailable ignition sources, such as refrigerators, running engines,electric motors, electric light switches and the like. However, gaswater heaters have sometimes been suspected because they often have apilot flame.

[0005] Any vapors from spilt or escaping flammable liquid or gaseoussubstances in a space in which an ignition source is present, provides apotential for ignition. “Fumes,” “extraneous gases” or “extraneousfumes” is sometimes hereinafter used to encompass gases, vapors or fumesgenerated by a wide variety of liquid volatile or semi-volatilesubstances such as gasoline, kerosine, turpentine, alcohols, insectrepellent, weed killer, solvents and the like as well as non-liquidsubstances such as propane, methane, butane and the like. Manyinter-related factors influence whether a particular fuel spillage doeslead to ignition. These factors include, among other things, thequantity, the nature and physical properties of the particular type ofspilt fuel. Also influential is whether air currents in the room, eithernatural or artificially created, are sufficient to accelerate the spreadof fumes, both laterally and in height, from the spillage point to anignition point yet not so strong as to ventilate such fumes harmlessly,that is, such that air to fuel ratio ranges capable of enabling ignitionare not reached given all the surrounding circumstances.

[0006] One surrounding circumstance is the relative density of thefumes. When a spilt liquid fuel spreads on a floor, normal evaporationoccurs and fumes from the liquid form a mixture with the surrounding airthat may, at some time and at some locations, be within the range thatwill ignite. For example, that range for common gasoline vapor isbetween 3% and 8% gasoline with air, for butane between 1% and 10%. Suchmixtures form and spread by a combination of processes including naturaldiffusion, forced convection due to air current draughts and bygravitationally affected upward displacement of molecules of one lessdense gas or vapor by those of another more dense. Most common fuelsstored in households are, as used, either gases with densitiesrelatively close to that of air (eg. propane and butane) or liquidswhich form fumes having a density close to that of air, (eg. gasoline,which may contain butane and pentane among other components is verytypical of such a liquid fuel).

[0007] In reconstructions of accidental ignition situations, and whengas water heaters are sometimes suspected and which involved spilt fuelstypically used around households, it is reported that the spillage issometimes at floor level and, it is reasoned, that it spreads outwardlyfrom the spill at first close to floor level. Without appreciable forcedmixing, the air/fuel mixture would tend to be at its most flammablelevels close to floor level for a longer period before it would slowlydiffuse towards the ceiling of the room space. The principal reason forthis observation is that the density of fumes typically involved is notgreatly dissimilar to that of air. Combined with the tendency ofignitable concentrations of the fumes being at or near floor level isthe fact that many gas appliances often have their source of ignition ator near that level.

[0008] The present invention aims to substantially lower the probabilityof ignition in typical fuel spillage circumstances.

SUMMARY OF INVENTION

[0009] The invention provides a gas water heater including a watercontainer adapted to be heated by a gas burner; an enclosure surroundingthe burner and the water container, the water heater being characterizedby having at least one opening adapted to allow air for combustion orextraneous fumes to enter the enclosure without igniting flammableextraneous fumes outside of the enclosure.

[0010] Preferably the at least one opening includes an aperture which iscovered by a flame trap, which prevents the burner igniting extraneousfumes outside of the enclosure; and an air inlet through which air forcombustion purposes is drawn.

[0011] Preferably the opening is remote from the gas burner and includesa duct for passage of air to the burner.

[0012] Preferably the opening and the aperture are collocated or are asingle item.

[0013] Preferably the at least one opening is covered by a flame trap.

[0014] Preferably the aperture is in the enclosure.

[0015] Preferably the aperture is positioned close to a lower end of theenclosure.

[0016] Preferably the aperture is positioned in a lower end of theenclosure.

[0017] Preferably the aperture is positioned below the burner.

[0018] Preferably the aperture is positioned to allow air and fumesoutside of the water heater to enter into an air passage leading to theburner.

[0019] Preferably the aperture allows air and fumes to enter the lowestpoint of the air passage.

[0020] Preferably one of or a combination of: a light detection orsensitive device; a flame detecting or sensitive device; a temperaturesensitive or detecting device; a heat detecting or sensitive device; andan oxygen depletion sensitive or detection device, is located in thewater heater to detect flame from the fumes if they have been ignitedinside the enclosure.

[0021] Preferably the at least one opening includes an air inlet whichis not covered by a flame trap, the air inlet having its lowest openingat a height of not less than about 500 millimeters or about 20 inches ormore from the bottom of the enclosure.

[0022] Preferably the at least one opening is located at or adjacent tothe highest point of the enclosure, if the enclosure has a height ofabout 500 millimeters or greater, from the bottom of the enclosure.

[0023] Preferably a snorkel device is provided to extend the at leastone opening to a height above the highest point of the enclosure.

[0024] Preferably the flame trap includes a heat resistant permeablematerial having high thermal capacity.

[0025] Preferably the flame trap includes a screen selected from eitherwoven or knitted mesh.

[0026] Preferably the flame trap is made of metal.

[0027] Preferably the flame trap is made of one of: steel, stainlesssteel, copper and aluminum.

[0028] Preferably a lint trap is included to wholly cover the apertureand the flame trap.

[0029] Preferably the lint trap is formed by mesh placed in the path oflint or dust travelling to the flame trap means.

[0030] Preferably the water heater includes a gas shut off means whichshuts off the gas supply to the burner and or a pilot burner if the airand fumes are ignited after entering the enclosure.

[0031] Preferably the gas shut off means includes a heat sensitivemeans.

[0032] Preferably the gas shut off means includes a flame sensitiveswitch.

[0033] Preferably the gas shut off means includes an oxygen depletionsensitive means.

[0034] Preferably the enclosure comprises a separable jacket and base.

[0035] Preferably the flame trap is provided at or as part of theconstruction of joining areas of the base to the jacket, or the jacketto other component or the base to other component or at any locationwhere the fumes could enter the enclosure.

[0036] Preferably the flame trap is inherent in or is formed by thejoining areas including either only gaps or apertures of a size smallenough to act as a flame trap.

[0037] Preferably the flame trap has been added to the joining area oris deliberately incorporated as part of the joining area.

[0038] Preferably the flame trap is a layer of metallic mesh cooperatingwith the joining area to achieve the flame quenching or arrestingfunction.

[0039] Preferably the flame trap is inside of the water heater.

[0040] Preferably the gas shut off means includes a light detectionmeans.

[0041] The invention further provides a water heater having a burneradapted to combust gas to heat a water container above the burner withinan outer enclosure having an opening to admit air required to combustthe gas; and including air and extraneous fume flow means co-operativewith the opening to reduce or eliminate a possibility of extraneousfumes adjacent the enclosure being ignited outside the enclosure by agas flame associated with the burner.

[0042] Preferably a fume detecting device is located in the water heaterto detect fumes after they have entered the enclosure.

[0043] Preferably the at least one opening is positioned close to alower end of the enclosure.

[0044] Preferably the at least one opening is positioned in a lower endof the enclosure.

[0045] Preferably the at least one opening is positioned below theburner.

[0046] Preferably the at least one opening is positioned so as to allowair and fumes outside of the water heater to enter into an air passageleading to the burner.

[0047] Preferably the at least one opening allows air and fumes to enterthe lowest point of the air passage.

[0048] Preferably one of or a combination of: a light sensitive device;a flame detecting device; a temperature detecting device; a heatdetecting device; and an oxygen depletion measurement device, is locatedin the water heater to detect flame from fumes after they have beenignited.

[0049] Preferably the flame trap is a flame quenching or arrestingmeans.

[0050] Preferably the device or devices are included in a gas shut offdevice.

[0051] Preferably one of or a combination of: a light detection orsensitive device; a flame detecting or sensitive device; a temperaturesensitive or detecting device; a heat detecting or sensitive device; andan oxygen depletion sensitive or detection device, is located in thewater heater to detect flame from fumes if they have been ignited insidethe enclosure.

[0052] Preferably device or devices are included in a gas shut offdevice.

[0053] The invention also provides a water heater having a burneradapted to combust gas to heat a water container above the burner withinan outer enclosure having an opening to air required to combust the gas;and including air and extraneous fume flow means cooperative with theopening to reduce or eliminate a possibility of fumes adjacent theenclosure being ignited outside the enclosure by a gas flame associatedwith the burner; the water heater including gas shut off means which hasa flame detecting or sensing device located in a path of flame externalto a combustion chamber of the water heater and also located in any pathof flame of fumes ignited in the enclosure.

[0054] Preferably the flame external to the combustion chamber is causedby flame spillage from the burner caused by a blockage of an exhaustflue.

[0055] Preferably the flame external to the combustion chamber is causedby air starvation in the combustion chamber.

[0056] One advantage of the invention is the provision of a barrier tothe unprotected entry, at the lower end of the jacket or enclosure, offlammable extraneous fumes. In alternative embodiments it provides aprotected entry means for such fumes near or at the base of theenclosure in which case these extraneous fumes are consumed in acontrolled manner. The protected entry is, in the most preferred form, aflame trap preventing ignition of the remaining fumes in the surroundingatmosphere or of any liquid remaining nearby.

[0057] An advantage of locating the air intake for combustion purposesabove the midpoint of the gas water system is that it reduces the chanceof extraneous fumes entering the heater via the air intake becausegenerally such flammables are heavier than air, which in the main do notattain dangerous levels at the air intake level.

[0058] The use of air close-off means and gas shut-off means activatedby a trigger provides the advantage of suffocating any flame in theheater, or switching off the gas supply, or preventing uncontrolled orundirected ignition of gases or vapors from exiting the heaterenvironment.

[0059] By providing an extended air intake, the risk of lint or dustaffecting the efficiency of the water heater is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] An embodiment of the present invention will now be described, byway of example only, by reference to the accompanying drawings in which:

[0061]FIG. 1 is a cross section through a gas water heater embodyingaspects of the present invention;

[0062]FIG. 2 is a cross section through a gas water heater similar toFIG. 1, with additional safety features (of flame trap and TSS);

[0063]FIG. 3 is a cross section taken through the line 111-111 of FIG.2;

[0064]FIG. 4 is a cross section through a gas water heater similar tothat of FIG. 2;

[0065]FIG. 5 is a cross section taken through line V-V of FIG. 4;

[0066]FIG. 6 is a cross section through a gas water heater with a safetyfeature (of air close-off means);

[0067]FIG. 7 is a cross section through a gas water heater of anotherembodiment of the present invention.

[0068]FIG. 8 is a cross section through a gas water heater of yetanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0069] Illustrated in FIG. 1 is an assembly of a storage type gas waterheater 2 including jacket 4 which surrounds a water tank 6, a mainburner 14 in a combustion chamber 15. The water tank 6 is preferably ofmains pressure capability and is capable of holding heated water. Thewater tank 6 is preferably insulated by foamed insulation 8. Alternativeinsulation may include fiberglass or other types of fibrous insulationand the like.

[0070] Located underneath the water tank 6 is the main burner 14 whichuses natural gas or other gases such as LPG, for example. The mainburner 14 combusts a gas and air mixture and the hot products ofcombustion resulting rise up through flue 10, possibly with heated air.Near the pilot burner 49, is a sheath 52, preferably made of copper,containing wires from a flame detecting thermocouple 51 which is a knownsafety measure to ensure that in the absence of a flame at the pilotburner 49 the gas control valve 48 shuts off the gas supply. Passingthrough the center of the tank 6 is a flue 10, in this instanceincorporating a series of baffles 12 to better transfer heat generatedby the main burner 14.

[0071] The products of combustion pass upwards and out the top of thejacket 4 via the flue outlet 16 after heat has been transferred from theproducts of combustion. The flue outlet 16 discharges conventionallyinto a draught diverter 17 which in turn connects to an exhaust duct 19leading outdoors.

[0072] Close to the height of the top of the jacket 4 and the flueoutlet 16 is an air inlet 18 through which air is drawn down the duct 22to the main burner 14. The duct 22 is suitably constructed from sheetmetal 20. In a non-illustrated alternative construction, a part or allof duct 22 may be inside the external cylindrical envelope of the jacket4.

[0073] The heater 2 is preferably mounted on legs 24 to raise the base26 off the floor. In the base 26 is an aperture 28 which is closed, butnot gas tightly, by a flame trap device 30 (which operates on a flamequenching principle). The flame trap 30 is preferably made from twoparallel sheets of mesh each about 0.010 inch diameter metal wirestrands woven into mesh having about 30 to 40 strands per inch. Mildsteel or stainless steel wire are suitable. Alternatively a portedceramic tile of the SCHWANK type (registered trade mark) can be utilizedalthough the recognized flame quenching ability of metallic woven orknitted mesh together with its robustness and ease of forming generallycommends its use. The tile type functions as a flame quenching trap aslong as the porosity is suitable.

[0074] A single layer of mesh or a porous ceramic tile may besusceptible to clogging by lint or other “blocking” materials such asdust or the like. Lint caught in the openings of a single mesh or a tilemight act as a wick which may allow flame, which would not otherwisepass through the flame trap, to do so. In this situation the flame trapdevice would tend not to function as efficiently. To prevent thistendency, the flame trap is preferably constructed with either twolayers of mesh or a layer of mesh and a tile. In this way the layer ofmesh further from the source of fumes acts as a flame trap and the layercloser to the source of fumes acts as a lint trap.

[0075] Where the base 26 meets the jacket 4, the mating surfaces 32(made up from surfaces of base 26 and jacket 4) can be sealed thoroughlyto prevent ingress of air or any flammable gas or vapor. In FIG. 1, themating surfaces 32 extend upwardly from the base 26 around the jacket 4.The cylindrical wall of jacket 4 (the majority of gas water heaters arecylindrical; however, a cubic shaped jacket 4 may be utilized) can besealed gas tightly so no openings or breaks remain upon assembly andinstallation. In particular gas, water, electrical, control, or otherconnections, fittings or plumbing, wherever they pass through the jacket4 or base 26, can be sealed airtight. The joining area (or matingsurfaces 32) of base 26 to jacket 4 and all service entries or exits tothe jacket 4 or duct 22 need not be sealed airtight providing they aredesigned and constructed being only minor surface to surface clearancesor gaps, each of which is capable of acting as flame quenching traps.The structure of such service entries or exits are known in the art andnot described herein. It is preferred, however, that the space aroundthe burner be substantially air/gas tight except for means to supplycombustion air.

[0076] Pilot flame establishment can be achieved by a Piezo-electricigniter. A pilot flame observation window can be provided which issealed. Alternatively, if the pilot is to be lit by removing or openingan access, safety interlocks (not illustrated) are included to ensurecomplete closure against unprotected fume access during heateroperation.

[0077] During normal operation, the heater 2 operates in the samefashion as conventional heaters except that most air for combustionenters at air inlet 18 and a small proportion through flame trap 30.However, if a spilt fuel is in the vicinity of the heater 2 then somegas or vapor from the spilt fuel is drawn in through the flame trap 30before it builds up to a level to enter via air inlet 18. Flame trap 30allows the combustible gas or vapor and air to enter but prevents flameescaping the jacket 4 or duct 22. The spilt fuel is burnt and exhaustedeither through the flue 10 via outlet 16 and duct 19 or through the duct22 and inlet 18 (which in this case will act as an outlet). Becauseflame cannot pass outwardly through the flame trap 30, any spilt fuelexternal to the heater 2 will not be ignited.

[0078]FIGS. 2 and 3 show an embodiment similar to that of FIG. 1. Likeparts use the same reference numbers as those of FIG. 1. In FIG. 2 thereis, adjacent the gas control valve 48, a flame sensitive switch 50 whichmay be inserted in the same circuit as the pilot flame detectingthermocouple 51.

[0079] The flame sensitive switch may be substituted by a light detectoror a heat detector. The flame sensitive switch can also be substitutedby a gas, fume vapor detection switch which will close off gas controlvalve 48 if a flammable fume is detected.

[0080] With reference to the cross section depicted in FIG. 3, the duct22 contains gas control valve 48 and the flame trap 30 is shown forminga bottom end of the duct. In fact, the flame trap 30 may be positionedspanning the bottom end of the duct 22 and an adjacent portion of thebase 26. An advantage from such a positioning of the flame trap 30,including that shown in FIGS. 2 and 3, by comparison with the centerposition of base 26 shown in FIG. 1, is that it permits the positioningof a flame sensitive switch 50 (FIG. 2) directly below the gas controlvalve 48 which is also an ideal position to detect flame spillage fromthe combustion chamber 15 which can occur if, for example, the flue 16,or exhaust duct becomes blocked. Similarly it is ideally positioned todetect flame spillage such as would occur due to air starvation if inlet18 were inadvertently blocked.

[0081] As shown in FIG. 3, opening 28 and flame trap 30 (including alint trap device as mentioned above) are at the base of the duct 22below the gas control valve 48 and flame detecting thermocouple 50 (seeFIG. 2). In this way, should fumes which enter through flame trap 30 beignited, a flame forms and burns on the inside surface of the flame trapand the flame detecting switch 50 actuates the gas control valve 48 toshut off the gas supply, thus removing it as a continuing source ofignition. After the pilot and main flames have been extinguished, anyvapors of spilt fuel continuing to enter through the flame trap 30 maycontinue to burn because of the initial ignition and resulting suctionof air and may continue to burn until there is insufficient flammablevapor remaining to be drawn in from the vicinity of the heater assembly2.

[0082] By providing an air inlet 18 at a high position above the base26, the more commonplace liquid fuels, the flammable gases and vaporsare far less likely to be available to a gas water heater flame.

[0083] In the water heater 2 of FIGS. 4 and 5, the path for air entry tomain burner 14 is provided by a combined flame trap and duct 54fabricated of metallic mesh 21. This arrangement provides that allcombustion air passes through a flame quenching surface 21 and theheight of the duct 54 need not be as high as the jacket 4 nor need itnecessarily extend upwardly. As evident in FIG. 5, it is preferablycomposed of the separated layers 21 a and 21 b of metallic mesh. Thistwo layer construction avoids any layer of lint, deposited externally,providing a possible combustion path through the mesh, as previouslyexplained.

[0084] Lint deposition in the openings of the mesh may be a cause ofgradual blockage. In due course such Tinting may cause starvation ofcombustion air. Therefore an extended surface area (along the fullheight of water heater 2 as depicted for instance) of the combined flametrap and air duct 54 may be of advantage for prolonging the time takenfor the duct 54 to become occluded with lint and for providing anadequate path for free induction of the air normally required forcombustion.

[0085] The positioning of gas valve 48 in its preferred position isshown in FIG. 5 outside of the duct 54. The entry of the gas pipe andthermocouple sheath into the duct 54 is effected so that if a hole isleft it is small enough either to be totally sealed or to act as a flamequenching trap.

[0086] The preference for the gas valve 48 outside the duct 54 is thatit provides one way of providing user access to the control knob and anybuttons on the gas control valve 48. It would be equally applicable incases where the duct 22 is made of imperforate sheet metal 20 as shownin FIGS. 1 and 2.

[0087] For ease of construction one option is that the gas pipe andthermocouple sheath can enter the water heater 2 via an opening in thejacket 4, bypassing completely the duct 54. This opening can be thensealed or if a gap is left, the gap is sized to act as a flame trap.However, whichever way the thermocouple sheath passes to enter thecombustion chamber, if it includes the flame sensitive switch 50 orother equivalent sensor, then it is greatly preferred that the flamesensitive switch 50 or other sensor is located in relation to theposition of the flame trap 30 so that the relative positions co-operatein the event of a flame from spilt fuel forms on the flame trap.

[0088] Illustrated in FIG. 6 is a another embodiment of the presentinvention, similar to that of FIG. 1, with like parts like numbered.This embodiment includes an anchor 34 which anchors a nylon line 36which is a heat sensitive frangible member. The nylon line 36 passesclose to the upper surface of the flame trap 30 and around a lowerpulley 38 then continues on to an upper pulley 40 around which it passesthrough 180 degrees, to make connection with a flap 42. The flap 42 isconnected by hinge 44 either to the inside of passage 22 or to a purposebuilt flange 46.

[0089] The flange 46, if it is utilized, can have a sealing medium(notillustrated) around it so that when the flap 42 makes contact with it,an air tight seal or a flame trap is formed. If the flange 46 is notutilized, the flap 42 can carry a seal so that, when released to move toa closed position, it will seal the inside of duct 22 to air tightquality or, in the alternative to form a flame trap. The flap 42 can bebiased towards the closed position by a spring, which is a preferredmethod, or alternatively the biasing can be by means of gravity. Ifdesired the flap 42 can be constructed from mesh, as described above toact as a flame trap.

[0090] In the embodiment of FIG. 6, when fumes from split fuel passingthrough the flame trap 30 are ignited, the heat of ignition breaking thenylon line 36, which is heat sensitive and frangible causing the flap 42to move to a closed position, shutting off air supply to the main burner14. This leaves no path down the duct 22 for air or combustible fumeswhich may have built up around the heater 2 to sufficiently gain accessto the main burner 14 and so the pilot burner 49 and the main burner 14may not have enough air available through the flame trap 30 to continueburning in which case the flame detection thermocouple 50 will cut offthe gas supply until manual intervention can restore it when a safeatmosphere is restored.

[0091] In conjunction with any form of the invention as shown in FIGS. 1to 6, a gas shut down facility similar to the above mentioned gas shutdown ability can be provided. In another form, the gas shut downfacility can be initiated by a flame sensitive switch (FSS) or athermocouple. Such a thermocouple is preferably located just inside ofthe flame trap 30 where ever it appears. FSS's are also used in waterheaters in circuit with the thermocouple (eg 50 of, FIG. 1) normallyprovided for confirming the establishment and retention of a pilot flameby raising an electric current flow to a level capable of keeping open agas supply to the pilot burner.

[0092] FSS's are used to reduce fire hazards in circumstances whereflame of the burner can “spill” through an air access opening adjacentthe main and pilot burners. In known FSS'S, the heat sensor isexternally positioned and in the present invention a FSS 50 ispositioned above the flame trap 30 in order to sense flame heat inputresulting from spilt flammable vapor burning on the inside of the flametrap 30 after having entered the combustion chamber through a possibleentry path. In the embodiment of FIG. 1 the preferred position of theFSS (not illustrated) is immediately above the flame trap and it ispreferred a small heat shield (not shown) be placed above the FSS toshield it from the normal radiant heat associated with the main burner14. In FIG. 2, the FSS (50) is positioned a short way above the flametrap 30.

[0093] In FIGS. 7 and 8 are illustrated a gas water heater 2 constructedsimilarly to that illustrated in FIG. 1. The heater 2 includes a base 26and jacket 4 which are either completely sealed (not illustrated) to airtight and flammable gas or vapor tight quality or alternatively, any gaspaths unsealed are fine enough to act as flame traps. In this instance,when completely sealed, all air for combustion is drawn in from the airinlet 18, and there is no means present to ignite any spilt fuel at thelower portions of the heater 2.

[0094] The embodiments shown in FIGS. 7 and 8 have no flame trap 30 oropening 28. However, an appreciable time delay will occur before gasesor vapors from spilt fuel rise to the elevated level of air inlet 18.Only then could the gases or vapors be drawn down passage 22 to the mainburner 14. Many spillages, nevertheless are quite minor in terms ofvolume of liquid spilt and in such cases the embodiment of FIG. 7 wouldtend to provide an adequate level of protection and that of FIG. 8 evenmore so. The air inlet 18, if it does not include a flame trap 30, wouldneed to be at least about 500 millimeters (20 inches) from the base 26(if the base 26 is near to the ground), in the presence of gasolinefumes (a different height may be required for other fumes). However, foradded protection a greater distance is preferred.

[0095] By providing an air inlet 18 at a high position above the base26, the more frequently used typical flammable fumes of spilt liquidfuels, are far less likely to be available to a gas water heater flame.

[0096] If the base 26 and jacket 4 has small gaps or openings limited intheir size in order to act as flame traps, then its operation will besimilar to the embodiment of FIG. 1. The features of FIG. 6 can beincorporated also with the embodiments described in FIGS. 7 and 8 whenthe base 26 and jacket 4 are sealed. In this instance, because the waterheater now includes a heat sensitive frangible member 36 located in anair passage in the vicinity of the main burner 14, if gases or vaporsignite having flowed down the passage 22 (which would indicate that thevolume of gases or fumes had risen to the level of air entry of the airinlet 18), the resulting flame would melt a frangible member such as thenylon line 36 in the vicinity of main burner 14. The nylon line 36 canbe connected in turn to a non-flammable and non-frangible section whichin turn makes connection with a spring biased flap similar to flap 42capable of sealing the passage 22. The distance between the nylon line36 and the flap is sufficiently long to close the passage 22, before aflame travelling back up the passage 22 reaches the flap. If the flap ishinged so that its closing motion is in the direction that flame wouldhave to travel to exit the passage 22, the hinging arrangement may beaided in closing by the movement of flame in a closing direction.

[0097] A further improvement to any of the above embodiments in theprevious paragraph is to provide a snorkel 60 as shown in FIG. 8extending the air inlet upwardly. The snorkel 60 allows air to be drawnto the main burner 14 but, by taking air from a height above the top ofthe jacket 4, will further reduce the risk of the heater 2 being anignition source of flammable gases or vapors from spilt fuel. If theheight of the jacket 4 is not greater than about 500 millimeters (20inches) above the base 26, the snorkel 60 can be used to draw combustionair from a more appropriate height, depending upon the spillage whichmay occur.

[0098] An additional level of hazard reduction is provided by theaddition of an oxygen depletion sensor in conjunction with the pilotburner (not illustrated). This makes available the entire airrequirement for the pilot flame to the pilot burner only through a pilotair duct (not illustrated), gas tightly separate from the air supplyduct 22 and the combustion chamber 15. The pilot air duct has an airintake external to the remainder of the water heater assembly,preferably low to floor level where water heaters are generallyinstalled, standing upright on a floor. At any convenient location inthe pilot air duct between the air intake end and the pilot burner is aflame quenching insert, composed of one or more of a variety of highthermal capacity gas porous heat resistant materials such as describedin relation to the flame trap 30. Locating the flame quenching insert ator near the air intake end is advantageous to make it accessible forcleaning of lint or dust that may accumulate in it. In the pilot airduct is also located an element sensitive to oxygen depletion in thepilot air duct.

[0099] With these features added to any of the embodiments of FIGS. 1 to7, the use of the oxygen depletion sensor reduces the risk of ignitionof escaping flammable vapor in particular when the pilot burner isalight but the main burner is not, by sensing oxygen depletion in theincoming pilot air supply if a flammable component it ignites in whichcase it would cause a gas control valve 48 of the type referred to inFIG. 1 to shut down gas flow to the pilot burner. The shut down providesa time period for flammable vapor to safely ventilate. Resumption ofnormal operation of the water heater requires human intervention but,even if done ill-advisedly, in any event the oxygen depletion sensorwould continue to deny the pilot burner of gas and the arrangement wouldbehave safely even with extraneous flammable fumes remaining near thewater heater. An oxygen depletion sensor can be used alternatively inplace of or in conjunction with the previously described flame sensingsensor 50 (FSS), and can be located similarly.

[0100] The invention thus far described can function at three levels ofsafety. The embodiment, as illustrated in relation to FIGS. 7 and 8,adds height and distance that fumes from spilt fuel must travel to reachthe main burner 14 or pilot burner 49. The second embodiment, asillustrated in FIGS. 1, 2, 3 and 6, adds not only height and distancebut also allows some and advantageously all the extraneous fumes toenter the base of the heater 2 and be consumed safely, conceivably untilall residual risk of fire and explosion is avoided by dissipation of thespillage.

[0101] The third level, as illustrated in FIGS. 4 and 5, adds a furtherlevel of confidence by protecting all air entry with a flame arrestor,recognizing that high levels of airborne lint or other dust may tend toblock the air intake and starve the burner of air for combustion if theair entry were not periodically cleared of that lint or other dust. Theembodiment of FIGS. 4 and 5 can be constructed to protect againstignition of all flammable gases and vapors outside of the enclosure orjacket regardless of the density of those gases and vapors relative toair.

[0102] Whilst the above embodiments are directed to room or indoorinstalled gas water heaters, the improvements described will function inan outdoor environment, if spillages occur nearby and fumes enter thegas water heater.

[0103] The foregoing describes embodiments of the present invention andvariations thereof and modification by those skilled in the art can bemade thereto without departing from the scope of the invention. Forexample, the flame trap may be located at various positions other thanthose shown in the drawings and described above. One alternativeposition is in the side of the combustion chamber opposite the gassupply. In such a construction the flame trap would be located in anopening in the skirt below the water tank and extending through thecorresponding portion of insulation.

[0104] In a further construction the flame trap is positioned above theheight of entry to the combustion chamber and the FSS is positionedabove that height of entry in the flow path of combustion air toward theburner. The aperture covered by the flame trap is in radiant heatcommunication with a FSS also positioned to be sensitive to flame rollout from flue blockage or combustion air starvation.

[0105] Further, the flame trap may be made from a variety of materialssuch as those described above, but can be fabricated from others notspecifically identified so long as they permit passage of air and fumesin one direction but prevent flames from travelling in the oppositedirection.

[0106] Suitable flame trap materials include those being porous, gaspermeable and possessing sufficiently high thermal capacity to quenchflame under typical conditions of use. Metallic structures having smallholes, made from, for example, mild steel, stainless steel, copper oraluminum are suitable and porous ceramics including glass or mineralwool woven or non-woven constructions are also suitable. Fibre matrixceramic is suitable as is flexible or rigid constructions.

[0107] Also, the air passage for combustion air, such as in thestructure labelled 22 in FIG. 1, can be located between water tank 6 andjacket 4. The passageway can be of a variety of shapes and sizes and canbe formed in and bounded by the insulation or can be formed by tubes,pipes conduits and the like.

[0108] Finally, main burner 14 and combustion chamber 15 can havedifferent constructions such as those described in U.S. Pat. Nos.4,924,816; 5,240,411; 5,355,841; and co-pending applications 08/333,871and 08/113,618, for example, the subject matter of which is incorporatedherein by reference.

What is claimed is:
 1. A gas water heater comprising a water containeradapted to be heated by a gas burner; and an enclosure surrounding saidburner, said enclosure having at least one entry means adapted to allowair and extraneous fumes to enter said enclosure without ignitingextraneous fumes outside of said enclosure.
 2. A water heater as claimedin claim 1 wherein said entry means includes an aperture which iscovered by a flame trap which prevents said burner from ignitingextraneous fumes outside of said enclosure; and an air inlet throughwhich air for combustion is drawn.
 3. A water heater as claimed in claim1 wherein said entry means is remote from said burner and includes aduct for passage of air to said burner.
 4. A water heater as claimed inclaim 2 wherein said entry means and said aperture are collocated or area single item.
 5. A water heater as claimed in claim 1 wherein saidentry means is covered by a flame trap.
 6. A water heater as claimed inclaim 2 wherein said aperture is in the enclosure.
 7. A water heater asclaimed in claim 2 wherein the aperture is positioned proximate to alower end of the enclosure.
 8. A water heater as claimed in claim 2wherein said aperture is positioned in a lower end of the enclosure. 9.A water heater as claimed in claim 2 wherein said aperture is positionedbelow said burner.
 10. A water heater as claimed in claim 2 wherein saidaperture is positioned to allow air and said extraneous fumes outside ofsaid water heater to enter into an air passage leading to said burner.11. A water heater as claimed in claim 2 wherein said aperture allowsair and said extraneous fumes to enter the lowest point of said airpassage.
 12. A water heater as claimed in claim 2 wherein one or acombination of: a light detection or sensitive device; a flame detectingor sensitive device; a temperature sensitive or detecting device; a heatdetecting or sensitive device; and an oxygen depletion sensitive ordetection device, is located in said water heater to detect flame fromsaid extraneous fumes if they have been ignited inside said enclosure.13. A water heater as claimed in claim 1 wherein said entry meansincludes an air inlet which is not covered by a flame trap, said airinlet having its lowest opening at a height of not less than about 500millimeters (20 inches) from a bottom portion of said enclosure.
 14. Awater heater as claimed in claim 1 wherein said entry means is locatedat or adjacent to the highest point of said enclosure, if said enclosurehas a height of about 500 millimeters or greater, from a bottom portionof the enclosure.
 15. A water heater as claimed in claim 1 wherein asnorkel device extends said entry means to a height above the highestpoint of said enclosure.
 16. A water heater as claimed in claim 5wherein said flame trap includes a heat conductive permeable material.17. A water heater as claimed in claim 5 wherein said flame trapincludes a screen made from woven or knitted mesh.
 18. A water heater asclaimed in claim 5 wherein said flame trap is made of either steel orstainless steel.
 19. A water heater as claimed in claim 5 wherein a linttrap is included to wholly cover said aperture and said flame trap. 20.A water heater as claimed in claim 19 wherein said lint trap is formedby mesh placed in the path of lint or dust travelling to said flametrap.
 21. A water heater as claimed in claim 1 further including a gasshut off means which shuts of gas supply to said burner and or a pilotburner if said air and extraneous fumes are ignited after entering saidenclosure.
 22. A water heater as claimed in claim 21 wherein said gasshut off means includes a heat sensitive means.
 23. A water heater asclaimed in claim 21 wherein said gas shut off means includes a flamesensitive switch.
 24. A water heater as claimed in claim 21 wherein saidgas shut off means includes an oxygen depletion sensitive means.
 25. Awater heater as claimed in claim 5 further comprising a jacketsurrounding said water container and said enclosure and a base locatedbeneath said enclosure.
 26. A water heater as claimed in claim 25wherein said flame trap is provided at or as part of the construction ofjoining areas of said base of said water heater to said jacket of saidwater heater, or said jacket to other components of said water heater orsaid base to other components of said water heater or at any locationwhere said extraneous fumes could enter said enclosure.
 27. A waterheater as claimed in claim 5 wherein said flame trap is formed by ajoining area of components of said water heater including either onlygaps or apertures of a size small enough to act as a flame trap.
 28. Awater heater as claimed in claim 26 wherein said flame trap has beenadded to the joining area or is deliberately incorporated as part ofsaid joining area.
 29. A water heater as claimed in claim 28 whereinsaid flame trap is a layer of metallic mesh cooperating with saidjoining area to achieve a flame quenching or arresting function.
 30. Awater heater as claimed in claim 29 wherein said flame trap is inside ofsaid water heater.
 31. A water heater as claimed in claim 21 whereinsaid gas shut off means includes a light detection means.
 32. A waterheater having a burner adapted to combust gas to heat a water containerabove the burner within an outer enclosure having an opening means toadmit air required to combust the gas; and including air and fume flowmeans cooperative with said opening to reduce or eliminate a possibilityof fumes adjacent the enclosure being ignited outside said enclosure bya gas flame associated with said burner.
 33. A water heater as claimedin claimed in claim 5 wherein a fume detecting device is located in saidwater heater to detect said extraneous fumes after they have enteredsaid enclosure.
 34. A water heater as claimed in claim 1 wherein saidentry means is positioned close to a lower end of the enclosure.
 35. Awater heater as claimed in claim 1 wherein said entry means ispositioned in a lower end of the enclosure.
 36. A water heater asclaimed in claim 1 wherein said entry means is positioned below saidburner.
 37. A water heater as claimed in claim 1 wherein said entrymeans is positioned to allow air and said extraneous fumes outside ofsaid water heater to enter into an air passage leading to said burner.38. A water heater as claimed in claim 37 , wherein said entry meansallows air and said extraneous fumes to enter the lowest point of saidair passage.
 39. A water heater as claimed in claim 37 , wherein one ofor a combination of: a light sensitive device; a flame detecting device;a temperature detecting device; a heat detecting device; and an oxygendepletion measurement device, is located in said water heater to detectflame from said extraneous fumes after they have been ignited.
 40. Awater heater as claimed in claim 5 wherein said flame trap is a flamequenching or arresting means.
 41. A water heater as claimed in claim 12, wherein said device or said devices are included in a gas shut offdevice.
 42. A water heater as claimed in claim 1 , wherein one of or acombination of: a light detection or sensitive device; a flame detectingor sensitive device; a temperature sensitive or detecting device; a heatdetecting or sensitive device; and an oxygen depletion sensitive ordetection device, is located in said water heater to detect flame fromsaid extraneous fumes if they have been ignited inside said enclosure.43. A water heater as claimed in claim 42 , wherein said device or saiddevices are included in a gas shut off device.
 44. A water heatercomprising a burner adapted to combust gas to heat a water containmentand flow means above the burner within an outer enclosure having anopening means to air required to combust the gas; and air and fume flowmeans cooperative with said opening means to reduce or eliminate apossibility of fumes adjacent the enclosure from being ignited outsidethe enclosure by a gas flame associated with said burner; said waterheater including gas shut off means having a flame detecting or sensingdevice located in a path of flame external to a combustion chamber ofsaid water heater and also located in any path of flame of said fumesignited in the enclosure.
 45. A water heater as claimed in claim 44wherein said flame external to said combustion chamber is caused byflame spillage from said burner caused by a blockage of an exhaust flueconnected to said combustion chamber.
 46. A water heater as claimed inclaim 44 wherein said flame external to said combustion chamber iscaused by air starvation in said combustion chamber.
 47. A water heatercomprising: means for storing or containing water; means forming achamber adjacent said storing or containing means; a burner located insaid chamber; and a flame trap associated with said chamber meanspermitting combustion air and extraneous gases, if present, into saidchamber and capable of preventing ignition of extraneous gases outsidesaid chamber.
 48. A water heater as claimed in claim 47 furthercomprising a separate opening in said means forming a chamber foringress of combustion air.
 49. A water heater as claimed in claim 47wherein said flame trap comprises a barrier selected from the groupconsisting of woven or knitted mesh, ported ceramic tile and heatresistant permeable materials of high thermal capacity.
 50. A waterheater as claimed in claim 47 further comprising a lint trap positionedto hinder contact of blocking materials with said flame trap.
 51. Awater heater comprising: a water tank; a combustion chamber locatedbelow said tank; a burner located inside said combustion chamber; aflame trap positioned in a portion of structure associated with saidcombustion chamber, said flame trap permitting ingress of air andextraneous gases, if present, into said combustion chamber and preventegress of flames from said structure.
 52. A water heater as claimed inclaim 49 further comprising a separate opening in said structure foringress of combustion air into said combustion chamber.
 53. A waterheater as claimed in claim 51 wherein said flame trap comprises abarrier selected from the group consisting of woven or knitted mesh,ported ceramic tile and heat resistant permeable materials of highthermal capacity.
 54. A water heater as claimed in claim 51 furthercomprising a lint trap positioned to hinder contact of blockingmaterials with said flame trap.
 55. A water heater as claimed in claim44 wherein said aperture is positioned above the height of said burnerand in communication with a downward path of combustion air toward saidburner.
 56. A water heater as claimed in claim 55 wherein a flamesensitive sensor is positioned between said flame trap and an opening tosaid combustion chamber to detect flame external to said combustionchamber caused by one of: flame spillage from said burner caused by ablocked exhaust flue connected to said combustion chamber; airstarvation in said combustion chamber; and extraneous fumes combustingbetween said flame trap and said combustion chamber.